Endothelin, which has been disclosed by M. Yanagisawa et al. (Nature, 332, P411, 1988), is an endothelium-derived 21-residue vasoconstrictor peptide and supposed that excessive secretion of endothelin may be involved in various diseases, such as hypertention, coronary ischemia, encepholapathy, nephropathy, circulation failure of various organs, and asthma. In Kokai 2-273625, TXA.sub.2 -receptor antagonist and inhibitor of TXA.sub.2 -synthetic enzyme etc. are disclosed as substances capable of inhibiting the increase in intracellular calcium ion concentration, which is caused by excessive secretion of endothelin. However, nobody has reported on substance capable of specifically inhibiting actions caused by endothelin, and so development of such a new compound has been desired.
Some compounds similar to the present compounds in chemical structure have already been known, however, there has been no report on the activity of those compounds as endothelin antagonist. For example, though 27-(3,4-dihydroxycinnamoyl-oxy)-3.beta.-hydroxy-oleanolic acid which is analogous to the compounds of the present invention has been reported by J. M. Koekemore et al. in JOURNAL OF THE SOUTH AFRICAN CHEMICAL INSTITUTE (27, P131, 1974), however, which has no description about the endothelin antagonist activity.